Miharasi tunnel located near the port Yokohama, is one of the typical OLD URBAN tunnel that needed reconstruction because of it's change to out of date from the recent traffic. However, for the sake of the geological conditions, the situation was hard to maintain the traffics during construction works. After various comparative examinations, a twin (couple) tunnel plan was successfully adopted with complicated constructive sequences. The total data obtained by long term and careful examination with the twin tunnelling, as well as the whole planning, would brought useful suggestion for another similar following plan.
